In vehicles, evaporative fuel which leaks into the ambient air from a fuel tank, etc., is described as one of causes of air pollution because of the large content of hydrocarbons (HC). In addition, the evaporative fuel is responsible for a loss of fuel. Accordingly, various techniques are known as a prevention thereagainst, and one known evaporative fuel controller (an evaporation system) is representative of one such technique. In the known controller, evaporated fuel from a fuel tank is released (purged) from a canister during operation of an internal combustion engine so as to be supplied to the engine. The canister contains an absorbent such as activated carbon.
In some of the above-described evaporative fuel controllers, the canister is provided between an evaporation passage, which is communicated to the inside of the fuel tank, and a purge passage which is communicated to an intake system of the engine. A purge valve is disposed substantially midway along the purge passage for controlling a quantity of evaporative fuel to the intake system in accordance with an operating state of the engine. In addition, the fuel tank is provided with a filler tube which has a filler passage formed therein for pouring fuel into the fuel tank. Further, the evaporation passage is provided with a refueling vapor control valve for controlling the evaporative fuel to be fed from the fuel tank to the canister, and further for controlling the internal pressure of the fuel tank.
An example of such an evaporative fuel controller for an internal combustion engine is disclosed, e.g., in published Japanese Patent Application Laid-Open No. 7-279788. The controller as disclosed in this publication includes the following: a shutter disposed on the top of the filler tube, the shutter being opened by a fuel-feeding nozzle being inserted into the filler tube; a vent tube for communicating the canister with an upper portion of the inner space of the fuel tank; a fuel supercharge-preventing valve positioned at an end portion of the vent tube, which end portion extends over the inside of the fuel tank; a vent cut valve provided substantially midway along the line of the vent tube for closing the line of the vent tube in response to opening and closing actions of the shutter; and a clearance provided on a side wall of the filler tube, the clearance communicating with an upper portion of the inner space of the vent tube. The evaporative fuel controller thereby prevents stoic of the fuel supercharge-preventing valve without respective increases in dimensions and weight of the same valve, and further prevents a liquid level in the filler tube from rising in response to an increase in temperature inside the fuel tank.
With conventional types of evaporative fuel controllers for the internal combustion engine, there is an inconvenience in that the inner pressure of the fuel tank and the like may cause blow-off of fuel through a filler opening of the fuel tank, or outflow of fuel supply emissions to the ambient air, immediately after fuel is poured into the fuel tank by means of the fuel-feeding nozzle.
In addition, since the refueling vapor control valve is held open during operation of the engine, then a large amount of evaporated fuel in the fuel tank is caused to flow into the canister. This causes another inconvenience in that the function of the canister is deteriorated, thereby reducing the durability of the canister and thus reducing the running performance of the engine, with a concomitantly adverse influence on exhaust gases. As a result, controllers of this type have failed to meet new regulations on exhaust gases.
There is also known an evaporative fuel-collecting device representative of another technique for preventing loss of fuel evaporation. In the evaporative fuel-collecting device, evaporated fuel from a fuel tank is released (purged) from a canister during operation of an engine so as to be supplied to the engine. The canister contains an absorbent such as activated carbon.
An example of such an evaporative fuel-collecting device is disclosed, e.g., in published Japanese Patent Application Laid-Open No. 7-34989. The device as disclosed in this publication includes the following: a first conduit line, whereby evaporative fuel generated in the fuel tank is guided into a canister device; a first valve disposed substantially midway along the first conduit line, the first valve being set to an open state when the internal pressure of the fuel tank fails to meet a predetermined value; a second conduit line arranged parallel to the first conduit line in order to introduce the evaporative fuel into the canister device; and a second valve disposed substantially midway along the second conduit line, the second valve being set to an open state until the internal pressure of the fuel tank falls below the predetermined value when the aforesaid internal pressure exceeds the predetermined value during operation of the engine. In the canister device, a length of a passage inside the canister from a first opening of the first conduit line differs from that from a second opening of the second conduit line in order to accommodate increased regulations of evaporative fuel and a drop in the internal pressure of the fuel tank.
In some conventional types of the evaporative fuel-collecting devices, an engine is disposed in a vehicle, and the vehicle is provided with a fuel tank as well, with a fuel-collecting canister disposed on the top of the fuel tank.
However, with a vehicle having the fuel tank spaced apart from a vehicular underbody by a small clearance, as seen in automobiles, when the canister is to be disposed on the top of the fuel tank, then loading and purging of butane into and from the canister, as required by statutory requirements of the U.S. Evaporation Regulations, are impossible to practice through the use of the aforesaid clearance. This causes an inconvenience of requiring removal of the fuel tank, which is disadvantageous in view of practical use.
In addition, since evaporation piping communicated to the aforesaid canister cannot be made larger in length, there is another inconvenience in that nothing accelerates fluidization of evaporation, thereby making it impossible to reduce the amount of absorption of evaporation into the canister.
Further, in engines for automobiles, an evaporative emission control system is used in order to prevent green gases from diffusing to the outside. Such green gases vaporize from a liquid level of fuel in a fuel tank.
As illustrated in FIG. 13, in conventional types of evaporative emission control systems, such vaporized gases in a fuel tank are introduced into a canister "a", and are then absorbed by activated carbon (charcoal) "b", which is packed in the canister "a". Then, the absorbed gases are released from the canister "a" when the engine is run. Such released gases are guided into an engine intake passage "d" through a purge passage "c", and are then combusted in cylinders. A purge valve "e" is controlled to determine as to whether or not the vaporized gases are introduced into the engine intake passage "d". (Refer to published Japanese Patent Application Laid-Open No. 53-27721, for example). In this connection, in the canister "a", the activated carbon "b" is retained in a state of being sandwiched between upper and lower sheets of mesh "f".
However, in conventional types of evaporative emission control systems, a problem occurs with a bottom type of canister such as the canister "a" in FIG. 13, or a horizontal type of canister such as a canister "g" in FIG. 14, if the activated carbon "b" is spilled in the canister "a" or "e". More specifically, particles "h" of the activated carbon are caused to pass through the purge passage "c", with the result that the purge valve "e" is clogged up with the particles "h" (on the exit side of a valve disc). Accordingly, adverse affects such as abnormal operation of the engine or aggravation of exhaust gases are likely to bring about.
A further problem with the aforesaid types of canisters in FIGS. 13 and 14 is that these canisters are constructed so as to encourage the activated carbon particles to be drawn into the purge valve "e" by purge air if the activated carbon is spilled in the canister.
In order to obviate the above problems as encountered in the past, an object of the present invention is to provide an evaporative emission control system capable of ensuring that activated carbon particles in a canister are prevented from flowing into a purge valve.